We have recently cloned macrophages from human bone marrow by expanding single colonies on repeated agar cultures and later transferring the cells to liquid phase cultures. These cells bore monocyte-related membrane antigens, were esterase rich, phagocytic, made C3 and C4, and initially expressed DR antigens. When they were DR+, 2 lines promoted and suppressed mixed lymphocyte reactions. Later, after loss of DR expression, all five clones suppressed. This unique capability to clone functional macrophages, permits us to address important questions about various macrophage functions in man. First, we want to develop fresh clones, now that the cloning technique has been worked out. The primary goal is to acquire additional clones that participate positively in immune respones. Efforts will be made to retain expression of DR antigens. Recent work siggests tjat ]jagpcutpsos. T-cell growth factor or supernates from mitogen activated lymphocyte cultures, might be helpful in that regard. The temporal relationship between loss of DR expression and failure to promote lymphocyte responses will be studied. The possibility that macrophages that lose the capacity to promote lymphocyte responses become suppressor cells, needs substatiation. Additional macrophage functions will be studied to see if these functions segregate with different clones. These functions include (a) chemotaxis, (b) bacteriocidal activity, (c) interleukin-1 production and (d) classical interferon production. Prostaglandins, which are synthesized by macrophages, modulate immune responses significantly. Metabolites of arachidonic acid, including prostaglandins, will be studied in detail using resting and stimulated clones of cells. Macrophages produce interleukin-1, which is a potent promoter of lymphocyte responses. They also release mediators of suppression. Preliminary data suggests that molecules of different size in supernates from our cultured clones, help or suppress lymphocyte responses. The possibility that some, or all, clones (including those that suppress) release interleukin-1 will be examined. Perhaps suppressor clones release both suppressor mediators and interleukin-1 with a net functional predominance of the former. Initial studies will be done to characterize mediators release by our clones.